To keep the following description simple, consideration is given by way of example mainly to a retractable bollard which serves, depending on whether it is retracted or not, either to allow or to prevent access to a given urban zone. However that example should not be considered as being limiting in any way, and the teaching of the invention can be applied to other elements of retractable street furniture of a wide variety of types, such as signposts, technical cabinets, containers, dust bins, etc.
Actuator-containing support devices for retractable bollards (or for other retractable items of street furniture) can be subdivided into two types: firstly devices having an electropneumatic or an electrohydraulic actuator which are themselves driven by a jack fed with fluid under pressure from a compressor, and secondly electromechanical devices, which constitute the category to which the present invention relates.
For example, one such device having an electrical actuator is described in FR-A-2 650 009, which describes a box installed in a pit in the ground and containing a retractable bollard that is deployed under the control of an "electrical jack" type electrical actuator, i.e. an actuator in which an electric motor drives a moving rod by means of a worm screw or of a screw-and-nut type mechanism. That actuator (which includes the electric motor, a stepdown gear train, a transmission, etc.) is located in a low position at the bottom of the box, and the vertical moving rod points upwards and is connected to a raisable plate carrying the bollard.
Given various limitations inherent to its structure, that prior art device is incapable of satisfying the ever more severe constraints that are imposed on apparatuses of that type by local authorities, and others.
Firstly, it is considered that such a device should not require a pit to be dug deeper than 80 cm so as to ensure that there is no risk of interfering with pipes, cables, etc. This means that the device must be very compact, particularly if it is desired that when the bollard or other item of street furniture is in the deployed position, it should be of sufficient height to enable it to act as an obstacle. In this respect, since the structure of the device of FR-A-2 650 009 has its actuator situated at the bottom of the box and surmounted by the moving plate that carries the bollard, the maximum possible height for the bollard is reduced to a value of less than half the depth of the pit receiving the box, and this is particularly constraining; thus, the text of that document mentions one meter as being a typical pit depth for receiving a bollard of height 400 mm, which proportions are inappropriate in most situations.
Secondly public safety constraints require the bollard to be capable of "fail-safe" operation, i.e. in the event of its electrical power supply being interrupted, particularly in the event of a power cut, a bollard that is in the raised position should move back down immediately and of its own accord into the retracted position, e.g. so as to ensure that emergency services have access. The retractable electrical bollard device of the above-mentioned document does not satisfy this requirement, and in the event of power failure the bollard is retractable only by hand (i.e. a person is required to actuate a mechanical device provided for that purpose on the bollard so as to cause it to retract back into its box); "fail-safe" in the meaning mentioned above would require the installation of backup batteries and of a mains power cut detection system to enable the bollard to return automatically to its retracted position in the event of a power cut. Such additional equipment would both complicate the design and maintenance of the bollard (in particular because of the batteries), and would also make it considerably more expensive, and even then it would not achieve total reliability since genuinely fail-safe operation must be capable of being achieved without relying on backup batteries.
Thirdly, it is highly desirable for the deployment or retraction speed of the bollard to be high, typically of the order of 2 seconds in either direction. Electropneumatic bollards satisfy this requirement well; in contrast, known electrical bollards do not enable such high speed to be achieved, with the time they require for deployment or retraction typically being about eight seconds, i.e. four times too long.
Fourthly, it is essential for the device to be protected against the risk of immersion in the event of water or mud collecting in the bottom of the box. The bottom of the box is naturally the region that is the most exposed and the most likely to collect unwanted infiltrations, in spite of the precautions that will normally be taken to drain fluids away. For this purpose, the device of the above-mentioned documents describes a complex structure designed to provide reinforced insulation for the motor and for the other portions of the electrical actuator, all of which are situated at the bottom of the box, in particular by means of a structure of concentric telescopic tubes that protect the actuator which is positioned axially.
Fifthly, given the very wide range of user requirements, it appears to be desirable to be possible to fit the support device with bollards or other items of street furniture that are highly variable as a function of demand, while nevertheless retaining a common universal basic support. It is also desirable to be able to change the bollard without difficulty, e.g. after a collision, and without that requiring the entire device to be changed. This means that it is necessary to have a lifting support structure which is essentially independent of the structure of the bollard, and that is not the case of the device in the above-mentioned document, where the above-mentioned design based on concentric telescopic tubes causes the structure of the bollard to be indissociable from the structure of the lifting device.
Sixthly, it appears in practice to be desirable to be able to power the device directly from mains voltage (220 V), rather than from low voltage (12 V or 24 V) so as to avoid the need for transformers, rectifiers, safety backup power supplies including storage batteries (see above), etc. However, direct power from mains voltage requires a structure which intrinsically avoids the electrical dangers that are associated with such direct connection to mains. Here again, given the structure of the device of the above-mentioned document, where the electrical components are located at the bottom of the box, it is necessary to provide feeds through a multitude of walls via sealing grommets or glands, thus complicating implementation and even then failing to provide maximum safety because it is still possible for water to infiltrate at all levels.
Finally, given their intended use, all such devices must naturally be very robust and very reliable in spite of severe operating conditions and rates, typically 600 maneuvers per day with maximum rates exceeding 120 maneuvers per hour.
The various requirements specified above are so constraining that, until now, no electrically retractable bollard has been capable of satisfying all of them.
That is why the market has been clearly dominated until now by retractable bollards that are electropneumatic, in spite of their greater complexity (due to the presence of electrical energy being transformed into pneumatic energy by means of a compressor), and in spite of being more difficult to install and maintain (since it is necessary to use personnel having a good understanding of the technology of pneumatic apparatuses).